1. Field of the Invention
This invention relates to a method of recovering dibutyltin difluoride from a hot, waste gas stream, and, more particularly, to a method of recovering dibutyltin difluoride as dry, solid particles.
2. Description of the Prior Art
Dibutyltin difluoride has been used extensively for making conductive tin oxide coatings by the powder deposition method. In this method, dibutyltin difluoride is reduced to a very fine particle size, which is then dispersed into a carrier gas stream, such as air. The stream then is delivered to a hot substrate, such as glass, and the desired tin oxide coating is formed thereon by decomposition of the dibutyltin difluoride. The powder deposition method is described in detail in U.S. Pat. Nos. 3,677,814; 4,182,783; 4,325,988; 4,344,986; 4,359,493; and 4,401,695.
Only a fraction of the dibutyltin difluoride actually is reacted with carrier and at the hot glass surface to form the conductive tin oxide coating; the rest, or unreacted dibutyltin difluoride, is removed by ambient air. This hot, waste gas stream contains spent dibutyltin difluoride which must be recovered. In practice however, commercial recovery of unreacted dibutyltin difluoride from the hot, waste gas stream is complicated by the fact that dibutyltin difluoride may be present in at least a partially molten state in the hot gas. Thus, when the gas stream is filtered through a fine porous filter bag, the molten dibutyltin difluoride tends to plug up the pores of the bag, making recovery very difficult. In an attempt to solve this problem, cool air has been introduced into the gas stream. However, this technique is disadvantageous because it dilutes the stream and thus it necessitates substantially larger filtration equipment to accommodate the increased volume of gas.
Accordingly, an object of this invention is to provide a method of recovering dibutyltin difluoride from a hot, waste gas stream.
Another object herein is to provide a method of recovering unreacted dibutyltin difluoride as substantially dry, solid particles.
A further object herein is to convert molten or partially molten dibutyltin difluoride, present in a waste gas stream, into substantially dry particles which can be readily recovered by filtration through a porous filter bag.
These and other objects and features of the invention are accomplished herein in a novel and commercially advantageous method, which is described in detail in the following description.